CVE-2026-89457: s390/dasd: Guard sysfs discipline callbacks against unallocated private data

CVE-2026-89457: s390/dasd: Guard sysfs discipline callbacks against unallocated private data

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

s390/dasd: Guard sysfs discipline callbacks against unallocated private data

Several sysfs show/store handlers call a discipline callback that
dereferences device->private, either directly or through the
DASD_DEFINE_ATTR() macro. During dasd_generic_set_online() the discipline
is assigned before check_device() allocates device->private, so an
unprivileged read of one of these world-readable attributes in that window
dereferences a NULL pointer and panics.

Guard the dereference inside each callback that actually touches
device->private.

The Linux kernel CVE team has assigned CVE-2026-89457 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.3 with commit c729696bcf8b23450043dd9c9972c15e53419ae4 and fixed in 6.12.109 with commit 536407b272402af679155910d7fdeeb4834eefb9
	Issue introduced in 5.3 with commit c729696bcf8b23450043dd9c9972c15e53419ae4 and fixed in 6.18.50 with commit 6452c13646af7c13d7f6668b6690cfb2427e7f7b
	Issue introduced in 5.3 with commit c729696bcf8b23450043dd9c9972c15e53419ae4 and fixed in 7.2.4 with commit 449f3bada7a9fad8b8cdf4bb20baf27ee9ca56c5
	Issue introduced in 5.3 with commit c729696bcf8b23450043dd9c9972c15e53419ae4 and fixed in 7.3-rc1 with commit 2a1780f9fc2493bd34c418a0be6fc58943afcecf

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89457
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/s390/block/dasd_eckd.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/536407b272402af679155910d7fdeeb4834eefb9
	https://git.kernel.org/stable/c/6452c13646af7c13d7f6668b6690cfb2427e7f7b
	https://git.kernel.org/stable/c/449f3bada7a9fad8b8cdf4bb20baf27ee9ca56c5
	https://git.kernel.org/stable/c/2a1780f9fc2493bd34c418a0be6fc58943afcecf